Linux 5.17 AArch64 Code Has SME Preparations, Adds KCSAN Support

While the Linux 5.17 merge window hasn't opened up yet, there have been a few early pull requests sent out this week ahead of this imminent next kernel cycle. One of those already sent out is the ARM64/AArch64 CPU architecture code updates for Linux 5.17.

Linux 5.17's 64-bit ARM code has a few feature items at play and a lot of code cleaning / preparations for future kernel cycles. This pull is just about the architecture work and not the Arm platform/DT updates for new SoC and hardware support, which will be sent separately as a PR during the merge window. The ARM64 updates for Linux 5.17 include:

- The Kernel Concurrency Sanitizer (KCSAN) is now enabled for ARM64. KCSAN is a race detector for the Linux kernel relying on GCC and Clang compiler instrumentation. KCSAN has already been supported on other architectures while 64-bit ARM is now part of the supported list.

- Clean-ups and preparations towards pringing Scalable Matrix Extensions (SME) to the kernel albeit not for Linux 5.17. Armv9-A's Scalable Matrix Extensions build on SVE/SVE2 for providing better and faster support around matrix operations. SME allows for matrix tile storage, load/store/insert/extract tile vectors, outer products of SVE vectors, a streaming SVE mode, and other improvements.

- Usage of SHA3 instructions for speeding up XOR.

- Perf subsystem updates for more Arm PMUs.

- Code clean-ups around atomics, BTI (Branch Target Identification), and other work.

- Various other code fixes and improvements.

See the ARM64 updates for the full list of arch changes for this next kernel cycle.